The problem is that python could be any number of applications, or even a background script. For example, if you use Screenlets, I believe the widgets are python processes. You can't remove python as it would disable a lot of important apps and scripts. If you want to stop leaking bandwidth, you can try what I've outlined in this Google+ post: https://plus.google.com/118226948467140990198/posts/YZhZJCZmGgm

The TL;DR version: block all TCP/IP traffic except those run by a new group you create. Then open a shell with access to that group and only apps you launch from that shell will have internet access. First create the group:

sudo groupadd internet

Now save this into a script and run it when you want to control bandwidth:

You might have to change the "192.68.0.1/24" bit to suit your local network. Now you will get a shell from which any apps you start (like firefox) will have internet access. The apps will still run under your username. All other apps will be blocked (unless they already have a persistent connection, in which case you will need to kill those processes).